DES_Update

Carries out the DES transformation function on a byte array according to the direction and mode set up by an earlier call to DES_Init() or DES_InitHex().

VBA/VB6 Syntax

nRet = DES_Update(hContext, abData(0), nDataLen)

C/C++ Syntax

Parameters

hContext

[in] handle to the DES context set up by an earlier call to DES_Init() or DES_InitHex().

lpData

[in,out] array containing the input data.

nDataLen

[in] equal to length of the input data in bytes.

Returns (VBA/C)

If successful, the return value is 0; otherwise it returns a non-zero error code.

.NET Equivalent

Des.Update Method (Byte[])

Remarks

The input data lpData must be an exact multiple of 8 bytes long. If not, an error code will be returned. Note that the output overwrites the input.

Example

' From FIPS 81 Appendix C
' AN EXAMPLE OF THE CIPHER BLOCK CHAINING (CBC) MODE
    Dim nRet As Long
    Dim hContext As Long
    Dim sCorrect As String
    Dim abKey() As Byte
    Dim abInitV() As Byte
    Dim abBlock() As Byte
    Dim vntPlain(2) As Variant
    Dim vntCipher(2) As Variant
    Dim i As Integer
    
    sCorrect = "683788499a7c05f6"
    abKey = cnvBytesFromHexStr("0123456789abcdef")
    abInitV = cnvBytesFromHexStr("1234567890abcdef")
    Debug.Print "KY=" & cnvHexStrFromBytes(abKey)
    Debug.Print "IV=" & cnvHexStrFromBytes(abInitV)
    
    ' The plain text is the ASCII code for "Now is the time for all ".
    ' We will store in an array of arrays (!)
    vntPlain(0) = cnvBytesFromHexStr("4e6f772069732074")
    vntPlain(1) = cnvBytesFromHexStr("68652074696d6520")
    vntPlain(2) = cnvBytesFromHexStr("666f7220616c6c20")
    
    ' Initialise context
    hContext = DES_Init(abKey(0), ENCRYPT, "CBC", abInitV(0))
    If hContext = 0 Then
        nRet = DES_InitError()
        Debug.Print "DES_Init Failed: " & apiErrorLookup(nRet)
        Exit Function
    End If
    
    For i = 0 To 2
        ' Get next block of plaintext from array
        abBlock = vntPlain(i)
        Debug.Print "PT(" & i & ")=" & cnvHexStrFromBytes(abBlock)
        nRet = DES_Update(hContext, abBlock(0), 8)
        Debug.Print "CT(" & i & ")=" & cnvHexStrFromBytes(abBlock)
        vntCipher(i) = abBlock
    Next
    Debug.Print "OK   =" & sCorrect
    
    ' Clear the context
    nRet = DES_Final(hContext)
    
    ' Now do in decrypt mode
    hContext = DES_Init(abKey(0), DECRYPT, "CBC", abInitV(0))
    If hContext = 0 Then
        nRet = DES_InitError()
        Debug.Print "DES_Init Failed: " & apiErrorLookup(nRet)
        Exit Function
    End If
    
    For i = 0 To 2
        ' Get next block of ciphertext from array
        abBlock = vntCipher(i)
        Debug.Print "CT(" & i & ")=" & cnvHexStrFromBytes(abBlock)
        nRet = DES_Update(hContext, abBlock(0), 8)
        Debug.Print "PT(" & i & ")=" & cnvHexStrFromBytes(abBlock) & " [" & StrConv(abBlock, vbUnicode) & "]"
    Next
    nRet = DES_Final(hContext)

This should result in output as follows:

KY=0123456789ABCDEF
IV=1234567890ABCDEF
PT(0)=4E6F772069732074
CT(0)=E5C7CDDE872BF27C
PT(1)=68652074696D6520
CT(1)=43E934008C389C0F
PT(2)=666F7220616C6C20
CT(2)=683788499A7C05F6
OK   =683788499a7c05f6
CT(0)=E5C7CDDE872BF27C
PT(0)=4E6F772069732074 [Now is t]
CT(1)=43E934008C389C0F
PT(1)=68652074696D6520 [he time ]
CT(2)=683788499A7C05F6
PT(2)=666F7220616C6C20 [for all ]

See Also

DES_Init DES_InitHex DES_UpdateHex DES_Final

[Contents] [Index]